Rotary atomizers are commonly used for coating components, such as automobile body parts, and are known, for example, from German Patent DE 94 19 641 U1. Such rotary atomizers have a pivoted bearing shaft driven by a turbine charged by compressed air and that carries a bell cup that rotates during the coating procedure with a high revolution. The bell cup is supplied with coating material (e. g. paint, varnish, etc.) through an internal paint tube, in which case the coating material is carried to the outside by centrifugal forces and sprayed through a circumferential spraying edge.
Furthermore, it is known to produce a spray stream from the bell cup by using steering air. For this purpose, the known rotary atomizer has an air steering ring on its front with circumferentially distributed air steering jets in an axial direction through which compressed air is blown that forms an air steering stream directed towards the external surface of the bell cup, thus forming the spray stream.
Rotary atomizers are also known in which the air-steering stream is not directed towards the external surface of the bell cup but towards the spray cone itself. Furthermore, it is possible to blow out of the air-steering stream in an oblique direction as to the rotation axis of the bell cup or even in radial direction, in which case, the “Coanda-effect” is taken advantage of, as known, for example, from German Patent DE 100 53 296 C2.
Furthermore it is known from several publications, such as European Patents EP 0 333 040 B1 and EP 1 367 302 A2, how to clean a rotary atomizer by introducing it together with the mounted bell cup into an automatic cleaning apparatus and then to spray it with a cleaning fluid inside the cleaning device.
However, this automatic cleaning procedure is problematic with known rotary atomizers with an air-steering ring as described and with similar atomizers, since the cleaning fluid or the coating material from the previous coating operation can penetrate into the ring-shaped annular gap space between the front facing the bell cup and the bearing unit of the bell cup containing the conventional air turbine (facing axially the internal surface in front of the air-steering ring.) During the subsequent operation of the atomizer for painting, the liquid filled into the annular gap space is blown out by the air exiting the air depot of the atomizer, in which case the object to be coated, e. g., a vehicle body, can be sullied and lead to paint errors. When cleaning the known rotary atomizer previously described the area between the bell cup and the air steering ring had to be left empty to prevent the penetration of cleaning fluid and coating material into the bearing unit. Therefore, automatic cleaning was difficult with known rotary atomizers and only possible within limits.
In German Patent Application DE 10 2005 015 604 a bushing-shaped shaft cover was proposed that covers the bearing shaft in mounted state at least partially in the annular gap area between bell cup and atomizer casing or air-steering ring. This shaft cover in the shape of a bushing prevents the penetration of cleaning fluid into the annular gap during automatic cleaning of the rotary atomizer. By this, penetration of cleaning fluid into the bearing unit can be prevented, which in an extreme case could lead to blockage of the bearing shaft. Since the characteristics and measures of German Patent Application DE 10 2005 015 604 may also be practical for the present invention, its publication is included into the present application by reference. However, even in this proposed solution a small annular gap remains between shaft and bushing-shaped shaft cover, through which the rinsing fluid could penetrate into the annular gap space between bearing unit and internal surface of the air-steering ring.
In German Patent Application No. 10 2005 015 604.5, which is assigned to the assignee of the present invention, there is proposed a steering air ring or bell cup for a rotary atomizer with at least one steering air jet for delivering a steering air stream and a rotary bearing shaft where, in axial direction between the bell cup and the steering air jet, a circumferential annular gap is located. A shaft cover in form of a bushing covers the bearing shaft when mounted at least partially in the annular gap area between the bell cup and the steering air jet.
In German Application No. 10 2005 055 154.8, which is also assigned to the assignee of the present invention, there is proposed a rotary atomizer where the annular gap space between the front surface of the bearing unit and the internal surface facing it axially or any other front element of the atomizer is sealed in a radial way internally against the externally accessible area of the shaft. The sealing element provided for this purpose is located along the internal circumference of the air-steering rings or front element and able to be attached to the front surface of the bearing unit in a way that it is elastically deformable.